Reversing valve for hydraulic reciprocating motor



June 28, 1960 K. L. RETHMEIER 2,942,534

REVERSING VALVE FOR HYDRAULIC RECIPROCATING MOTOR Filed March 24, 195

FIG. 5

INVENTORI KAREL L. RETHMEIER BY: 14/ D. k

HIS ATTORNEY 2 Sheets-Sheet 2 REVERSING VALVE FOR HYDRAULIC RECIPROCATING MOTOR Karel Lodewijk Rethmeier, Delft, Netherlands, assignor toShell Oil Company, a corporation of Delaware Filed Mar. 24, 1958, Ser. No. 723,586

Claims priority, application Netherlands Mar. 26, 1957 1 Claim. (Cl. 121-465) The object of the invention is to overcome this drawback. v

To this end, according to the invention, one or more throttling passages are arranged in each valve face of theslide valve and/ or in the part of the slide face working in conjunction therewith, the length of each throttling passage being at least equal to the width of the valve face," measured in the direction of travel of the slide valve.

As a result of the above arrangement, when the slide valve is reversed, the supply pressure prevailing in one cylinder. space gradually passes over into the exhaust pressure, whereas the exhaust pressure prevailing in the other cylinder space is, gradually converted into the supply pressure. Consequently, whenthe direction of move-1 ment of the piston isreversed, there are no sudden changes in pressure in the two cylinder spaces, asshown byviolent impacts against the piston and the parts connected therewith, and against the cylinder covers- The throttling passages are preferably formed "by;

grooves arranged in the slide face in such a waythat each cylinder port leads into a groove or set of grooves, sub-' stantially in the middle thereof. p p

In order to prevent unnecessary leakage losses through the throttling passages it is preferable to choose a width of each slide valve face working in conjunction with a cylinder port and increased by its stroke, which is larger than the distance between the ends of the groove(s)' arranged in the slide face near this cylinder port; the width of the valve face and the said distance are measured in; the direction in which the slide valve face concerned.

moves over the slide face.

Prior attempts have been made to reduce the rate at which the hydraulic medium is supplied to or withdrawn from the cylinderspace when the slide valve is reversed by throttling the supply or exhaust by means of narrower grooves or channels arranged in the slide valve. By the above means the impacts are somewhat deadened, but they are not eliminated, since owing to the slight compressibility of the hydraulic medium, even the supply or discharge of an extremely small quantity of hydraulic medium to or from the closed cylinder spaces will result in a rapid rise or fall in pressure and an impact will consequently occur.

The way in which the occurrence of impacts in a hydraulic motor is prevented, according to the invention, will be more fully understood from the following detailed description and by reference to the accompanying drawing.

w t: A

in section of hydraulic reciprocating motor valve mecha- Figure 1 is a schematic diagram: showing an; elevation nism and associated parts. g

Figures 2, 3 and 4 are schematic diagrams showing the. valve mechanism of Figure 1 at various positions of the slide valve. Figures la, 2a, 3a, and 4a are'pressure'diagrams show-' ing pressure conditions pertaining at the positions of the slide valve in Figures 1, 2, 3, and 4, respectively, with configurations of the valve shown. j

Figure 5 is an elevation in section of analtemate form of valve mechanism with the 'slide valve in one extreme position of travel.

Figure 6 is an elevation in section of'the'valve mechanism of Figure 5 showing the slide valve in an intermediate position.

' end to a space (not shown) from where hydraulicmedium I Conduits or channels '4 and 5 connect the cylinder spaces A and B to the cylinder ports 7 and 8, respectively, which lead into the slide face 6. Moreover, a supply port 9 for the hydraulic medium also leads into the slide face, which supply port is connected at the other:

is supplied under high pressure P,..

The slide valve 10rests with the valve faces 11 and 12- I on the-slide face 6,'which' two 'valve faces are provided with grooves 13. and 14, respectively. .These grooves con J nect the space 15 between the valve faces 11 and 12 to the connected to the exhaust line, a leakage current will flow through the two throttling passages 13 and 14; Thepres ports has been ignoredinthe' pressure .diagrain 'ind ig 'part 16 ofthe slide valve chestlying outside theslide valve and connected by means of a conduit (not shown) to a space in which lowfpressure "P .prevails.

In Figure lthe slide valve 10.is in the middle position, i.e.,.it is placed symmetrically in relation to the cylinder ports 7 and 8. Since a pressure P, prevails in the space 15 between, thevalve faces :11 and 12-of the slide valve, which space is connected to the supply line, 9, and a pressure P smaller than P prevails in the space 16 which. is'

sure drop caused by this leaka'ge current is shown 'gra-zphicallyin Figure 1a. This diagram and the symmetricalposition of the slide valve in relation to the cylinder ports show that when the slide valve is in the position shown in.

Figure 1 ,1the pressure P in the cylinder space A is equal to the pressure P in the cylinder space B. Forthe sakeof simplicity, the effect on the pressure drop of the reduc-' tion of resistance inthe throttling passages at'the cylinder? ure 1a and inthe other pressure diagrams of the'drawingi .'In Figure 2, the slide valve 10 is in one of its extreme i I positions. The cylinder port 7 leading to the-'cylinder space A, is then fullyfopened'and, if the pressureslosse's 1 .7 a resulting from theiflow Ofithe medium through -theports" are ignored, the pressure P prevailing in this space A- will be equal to the dischargepressure P The cylinder port 8 -leading to the cylinderspace B is also fully opened;-

and as this, port 'is in communication with thesupply port 9 via the space 15, the pressure P prevailing in the cylin-' der space B is equal to the supply pressure P if the pres-' sure losses resulting from the How of the medium throughthe passages are ignored. The pressure drop inthe throttling passages 13 and 14 is shown graphically; f

As a result of the difierence in pressure prevailing over i the piston, the latter moves in the cylinder. At the end of its stroke the direction of motion should be reversed, this being efiected by reversing the slide valve 10 from its extreme position shown in Figure 2 to the opposite V extreme position illustrated in Figure 4 in which the two Patented June cylinder ports 7 and 8 are again fully opened, but in which position the cylinder port 7 is now connected to the space 15, so that the supply pressure P prevails in the space A, and the cylinder port 8 is connected to the exhaust space 16, so that the discharge pressure P prevails in the space B. a

On account of the presence of the throttling passages 13 and 14, which during the reversal of the slide valve move across the cylinder ports 7 and 8, respectively, the pressure in the cylinder spaces A and B changes gradually. Figure 3, in which the slide valve 10 is shown in an intermediate position, shows that during the movement of the slide valve in the direction shown by the arrow, the cylinder ports 7 and 8 are successively connected to ad jaeent points of the throttling passages 13 and 14, respectively, so that during the sliding movement the pressure in cylinder port 7 gradually increases from P to P whereas the pressure in the cylinder port 8 gradually decreases from P to P As a result of the slight compressibility of the hydraulic medium, only a small quantity of medium will flow respectively into and out of the cylinder spaces A and B during these changes in pressure. so that the changes in pressure in the cylinder spaces A and B respectively may be considered equal to the changes in pressure occurring in'the cylinder ports 7 and 8. Consequently, as in these cylinder spaces too the pressures change uniformly, no impacts will occur in the cylinder spaces during the reversal of the slide valve. The pressure drop over the lengths of the throttling passages 13 and 14 is somewhat affected by the medium flowing into and out of the cylinder ports 7 and 8 respectively, during the sliding movement; however, the pressure drop remains continuous, so that the shock-free reversal of the direction of motion of the piston is not affected by it. During the reversal of the slide valve from the position illustrated in Figure 4 the pressure in the cylinder spaces changes in the opposite direction. r

In the same way as shown in Figures 24, the direction of motion of the piston can be reversed in a shock-free way by means of a device in which the throttling passages are formed by grooves arranged in the slide face 6. In another further embodiment the throttling passages may be formed by grooves arranged in the valve faces of the slide valve 10, which grooves work in conjunction with the grooves arranged in the slide face 6.

- The application of the invention is not limited to any one type of slide valve; the slide valve may be one with either internal or external admission, it may contain either a reciprocating or aturning movement and have fiat or cylindrical valve faces.

In Figures and 6 a device is illustrated according to the invention in which the throttling passages are arranged in such a way that there will be no leakage currents through these throttling passages if the slide valve is put in one of its extreme positions, which results in a greater hydraulic efficiency of'the motor.

- Figure '5 shows a slide valve case 17 in' which a cylindricalslide valve 18 can be moved to and fro by means of a slide valve spindle 19. The throttling passages are formed by grooves 23 and 24 arranged in theslide'face 20 at the cylinder ports 21 and 22. Between the cylinder ports 21 and 22 a supply port 25'is arranged for supplying the medium under high pressure P which supply port 25 is always in communication with the space 28 arranged between the valve faces 26 and 27 of the slide valve 18. The hydraulic medium is discharged through the spaces 29 lying outside the slide valve, which spaces are connected to a space (not shown) in which a low pressure P prevails.

In Figure 5 the slide valve 18 isin one of its extreme positions in which the left-hand ends of the grooves 23 and 24 are closed. The pressure in the cylinder port 21,

which is in communication with the cylinder space A, is then equal to the supply pressure P whereas the pressure in the cylinder port 22, which is in communication with the cylinder space E, is equal to the discharge pressure P As the grooves 23 and 24 are closed at one end, no leakage current flows through the throttling passages formed by these grooves when the slide valve is in its extreme position as shown in the drawing.

If, however, the slide valve 18 is moved to the right in order to reverse the direction of motion of the piston, both throttling passages are opened (see Figure 6) and as a result of the leakage current flowing through these throttling passages there will be a gradual pressure drop in the passages. A part of the leakage current through the throttling passage 24 is supplied via the cylinder port 22 to the cylinder space B adjacent to this port 22, as a result of which the pressure in this cylinder space gradually increases from P to P during the displacement of the slide valve 18, while sufiicient hydraulic medium is supplied through the cylinder port 21 from the cylinder space A to the leakage current flowing through the throttling passage 23 for the pressure in this cylinder space to gradually decrease from P to P during the displacement of the slide valve 18.

Immediately before the slide valve has reached its opposite extreme position the change in pressure in the cylinder spaces is completed. In this second extreme position of the slide valve the other ends of the throttling passages 23 and 24 are closed by the valve faces 26 and 27 of the slide valve, so that during the displacement of the piston there isno leakage current through the throttling passages. During the reversal of the slide valve from this extreme position, the pressure in the cylinder spaces changes, in the opposite direction.

The throttling passages in the extreme position of the slide valve as shown in Figure 5 is closed by choosing a width of each slide valve face working in conjunction with a cylinder port and increased by its stroke which is larger than the distance between the ends of the groove arranged in the slide face near this cylinder port; this width is to be measured in the direction in which the slide valve face moves over the slide face.

I claim as my invention:

In a hydraulic reciprocating piston motor, a reciprocating valve operating in the extreme positions of the motor piston, a casing having a slide face and valve ports communicating with the slide face through which hydraulic fluid may flow to actuate said motor piston, said reciprocating valve having valve faces disposed in sliding contact with said slide face throughout the entire length of travel .of the reciprocating valve, said valve faces being wider than said valve ports and being movable over said valve ports, and throttling channels between said valve faces and said slide face, said throttling channels each having an effective length at least equal to the width of its valve face and being located so as to intersect a valve port during movement of said reciprocating valve.

References Cited in the file of this patent UNITED STATES PATENTS 2,380,705 Procter July 31, 1945 2,675,024 Clark Apr. 13, 1954 2,751,752 Metcalf June 26, 1956 2,796,851 Ziskal June 25, 1957 FOREIGN PATENTS 231,630 Switzerland July 1, 1944 

